The present invention relates to the preparation of perfluoroalkanecarboxylic acids, and more particularly, it relates to the preparation of such acids with the formula R.sub.F COOH, wherein R.sub.F is a straight-chain or branched perfluoroalkyl radical containing from one to 20 carbon atoms, through intermediate perfluoroalkanedichloroethylenes, some of which are novel.
These acids, the salts of which are employed as surface-active agents in tetrafluoroethylene polymerization or as emulsifiers in foams for firefighting, are prepared commercially by electrofluorination of alkanesulfonic acid chlorides or by hydrolysis of perfluoroiodoalkanes, R.sub.F I, with oleum. However, this latter method results in the loss of two fluorine atoms per molecule of the perfluoro-iodo derivative.